The handover technology in a wireless communication network refers to, when a terminal moves, after accessing network via a certain base station, to the coverage area of another base station due to mobility of the terminal, a technology of process where the another base station is taken as a serving base station of a terminal to provide network access service to the terminal. In addition to a conventional hard handover, handover methods specified in IEEE 802.16e standard also comprise two soft handover methods, i.e. Macro Diversity Handover (MDHO) and Fast Base Station Switching (FBSS). In the two soft handover methods, a plurality of base stations need to be combined as a diversity set (DS) of a terminal. The terminal establishes connections with all the base stations in the diversity set, and adds a certain base station into the diversity set or deletes a certain base station from the diversity set according to signal strength changes of the base station during handover.
It is specified in the current IEEE 802.16e standard that a base station supporting MDHO or FBSS needs to send two thresholds H_Add (addition threshold) and H_Delete (deletion threshold) via broadcasting. When detecting the Carrier-to-Interference-and-Noise Ratio (CINR) of a certain base station is more than H_Add, the terminal will add the base station into its diversity set; when detecting the CINR of a certain base station in the diversity set is less than H_Delete, the terminal will delete the base station from its diversity set.
The above method for setting handover diversity set thresholds is a static thresholds method. However, the actual network condition is that the strengths of network signals differ in different time points or places; i.e. sometimes the network coverage is comparatively good and the CINRs of all adjacent base stations are comparatively high; while sometimes the network coverage is comparatively bad and the CINRs of all adjacent base stations are comparatively low. When the static thresholds method is applied, in a condition of either good or bad network coverage, the value of H_Add or H_Delete should neither be too high nor too low. If the value of H_Add or H_Delete is too high, in a condition of the bad network coverage, it may occur that none of the CINRs of adjacent base stations can reach H_Add, and thus those base stations can not be added into the diversity set; moreover, the base stations in the diversity set are more likely to be deleted since their CINRs are less than H_Delete which leads to a handover loss. If the value of H_Add or H_Delete is too low, in a condition of the good network coverage, it may occur that the CINRs of most adjacent base stations exceed H_Add; moreover, all the base stations in the diversity set are remained since the CINRs of these base stations are all more than H_Delete, resulting in excess of base stations added into the diversity set and waste of network resources.
As stated above, the current methods for setting handover diversity set thresholds are not flexible enough during implementation. Handover thresholds can not be optimized flexibly according to the actual condition of the network, and thus can not be dynamically adapted to the actual conditions of the network.